Nearly all of the lower aliphatic ketones, from acetone to dipentyl ketones, have been evaluated individually for the solvent dewaxing of lubricating oils. In an article by J. L. Tiedje and D. M. Macleod entitled "Higher Ketones as Dewaxing Solvents" in the early 1950's, three parameters which have an impact on the viability of these ketones were considered. J. L. Tiedje et al, Journal of the Institute of Petroleum, Vol. 41 (January 1955) pps. 37-43.
Essentially the authors teach that the three most important factors to consider in selecting a ketone, even one used in a pure state (i.e., no toluene), are: (1) the miscibility of the concerned aliphatic ketone with the lubricating oil, (2) the lowest possible solubility for wax in the concerned aliphatic ketones and (3) the highest filter rate possible to treat the oil-ketone effluent material.
From a miscibility standpoint the larger ketones were found to be better solvents than the smaller ketones, such as methylethyl ketone or acetone. The normal ketones were taught as preferred over the isoketones. And, methylisopropyl ketone was specifically taught as being inferior for dewaxing relative to methyl-n-propyl ketone because of this miscibility temperature disadvantage. The smaller ketones have the lowest wax solubility and the highest dewaxing temperature for a given pour point. From a standpoint of wax solubility per se, acetone and methylethyl ketone were by far the best dewaxing solvents. However, in light of their determined high miscibility temperatures, the overall choice for a dewaxing solvent was methyl-n-propyl ketone followed by diethyl ketone and methylisobutyl ketone. Methylisopropyl ketone was noted as having the lowest wax solubility except for methylethyl ketone and acetone, which as above-mentioned, proved totally unsatisfactory in regard to its miscibility temperature. It was also determined that as molecular weight increased, a rapid drop in filter rate was observed. Consequently, the lighter ketones were found to possess the best filter rates with pure methylethyl ketone outperforming the other alkyl ketones. There was however no recognition or teaching of the viable use of methylisopropyl ketone in combination with a catalytic dewaxing technique, the latter of which was developed and refined subsequent to the date of this article. There was also no recognition or teaching of the viable use of methylisopropyl ketone in admixture with other components, e.g. aromatic hydrocarbons.
In 1975, U.S. Pat. No. 3,902,988 issued to Bennett et al, relating to a process for the production of a range of lubricating oils derived via splitting a petroleum fraction. The light fractions are treated by catalytic dewaxing and solvent extraction while the heavy fractions are treated by catalytic hydrogenation and solvent dewaxing. The lighter petroleum fractions are passed in the presence of hydrogen over a mordenite catalyst of crystalline configuration having incorporated therein either a Group VIA and/or Group VIII metal. The heavy petroleum fractions derived are subjected to catalytic hydrogenation and subsequently to solvent dewaxing. The solvents contemplated for the solvent dewaxing process are alkyl ketones wherein the alkyl groups possess from 1 to 4 carbon atoms. Of particular preference in the solvent dewaxing procedure are methylethyl ketone, methylisobutyl ketone and mixtures of the same. It is also taught that these ketones may be present with either benzene or toluene in an amount of from about 25 to about 75 weight volume of the total solvent. There was no recognition, however, that a catalytic dewaxing unit can be most advantageously utilized downstream of a solvent dewaxing unit using methylisopropyl ketone as one of the subject solvents with toluene.
In 1972, U.S. Pat. No. 3,684,691 issued to Arey Jr., et al, relating to a process for combinative catalytic and solvent dewaxing. The catalytic dewaxing transpires upstream of the solvent dewaxing step. Crystalline aluminosilicate zeolites convert normal paraffins in the hydrocarbon oil to products easily removed from the low pour point oil. The patentees actually reverse the sequence of dewaxing as this disclosure relates to the instant invention.
In 1974, U.S. Pat. No. 3,816,295 issued to Coleman et al, relating to a process for simultaneous solvent refinement of a vacuum residuum with hydrocracking to eliminate waxy materials. The catalytic dewaxing and solvent dewaxing are taught as disjunctive embodiments. The dewaxing agent in the solvent dewaxing step is taught as a mixture of 40 to 60% by volume of a ketone such as acetone, methylethyl ketone or normal butyl ketone and about 60 to 40 volume percent of an aromatic compound such as benzene or toluene.
In U.S. Pat. No. 3,755,138 a combinative solvent and catalyst dewaxing unit is disclosed with the solvent dewaxing occurring upstream of the catalyst dewaxing process with the solvent dewaxing being carried out by well-known techniques, i.e. use of methylethyl ketone-toluene; methylethyl ketone-methylisobutyl ketone. There is a total lack of appreciation of using (and the advantages derivative thereof) a dewaxing solvent consisting of pure methylisopropyl ketone or methylisopropyl ketone in admixture with an aromatic hydrocarbon upstream of catalyst dewaxing.
In U.S. Pat. No. 3,960,705, a method of converting Foots oil (the by-product of a high quality wax dewaxing process) is disclosed to prepare a higher quality lubricant by subjecting same to catalytic hydroprocessing with a ZSM-5 zeolite under hydrogen pressure with downstream distillation. The preliminary ketone extraction is usually performed in the presence of methylethyl ketone; no awareness is evidenced or any generic or specific teaching is existent of the beneficial interaction of use of methylisopropyl ketone as the solvent dewaxing ketone in conjunct association with downstream Foots oil hydrocatalytic conversion to produce an oil of higher quality.
In conclusion, these prior disclosures have failed to teach or appreciate an energy efficient process derived from the combinative use of methylisopropyl ketone as the solvent (in conjunction with an aromatic hydrocarbon if so desired) when solvent dewaxing is employed in series, upstream and concomitant with catalytic dewaxing.